Increasing the average power of lasers is desirable for many industrial applications such as welding and cutting. However, while it has been possible to develop lasers with high peak power in the mega-watt range and higher (see, for example, A. F. Gibson and M. H. Key, High Power Lasers, Rep. Prog Phys , Volume 43, 1980), instability in the laser plasma has prevented maintenance of the high power so that average powers are typically in the single digit kilowatt range.
In order to obtain the higher peak intensities required for "thicker section" processing, lasers have often been operated in a repetitively pulsed manner. However, to be commercially viable in a typical commercial application, such a pulse machine must also possess a high production capability. Consequently, the ability to provide pulse as well as CW radiation, while still retaining high average power output, is becoming an increasingly important requirement in high powered industrial laser systems.
In low or medium powered lasers, pulse performance is normally accomplished through the utilization of a suitable switch to "chop" the dc electrical supply to the device. Operating a CO.sub.2 gas discharge in this manner has yielded output power levels 2 or 3 times higher than that attainable under regular CW conditions.
Such pulse lasers are known in the art, as described, for example, by James P. Reilly, Pulser/Sustainer Electric-discharge Laser, J. Appl. Phys., Volume 43, No. 8, Aug. 1972; Alan E. Hill, Continuous Uniform Excitation of Medium Pressure CO.sub.2 Laser Plasmas by means of Controlled Avalanche Ionization, Appl. Phys. Lett., Volume 22, No. 12, June 15, 1973; and Sequin et al, U.S. Pat. No. 4,288,758, issued Sept. 8, 1981 (describing an earlier invention by one of the inventors of the present invention).
Pulsed operation of most kilowatt lasers, however, is not practical. This is mainly because long life, high average power, switching devices, capable of handling the enormous pulse excitation energies associated with these large volume machines, are not available.
To overcome these disadvantages, the inventors have developed a completely different discharge switching technique known as burst mode operation to provide long term pulsed operation of a high powered laser. As particularly described here, the burst mode operation has been applied to a multi-kilowatt, photo-initiated, impulse-enhanced, electrically excited CO.sub.2 system (hereinafter PIE laser).